Former Speaker of the House Newt Gingrich, the frontrunner for the Republican nomination for president in 2012, has vowed to support a federal constitutional amendment that would ban same-sex marriage.

Gingrich’s pledge came in a written response to conservative Iowa group The Family Leader’s “The Marriage Vow — A Declaration of Dependence Upon Marriage and Family.” The group’s 14-point pledge can be found at http://www.thefamilyleader.com/the-marriage-vow.

In addition to opposing same-sex marriage, the pledge also requests candidates vow “personal fidelity” to their spouse, appoint federal judges who are “faithful constitutionalists” and reject Islamic sharia law.

Gingrich, 68, has been married three times. In 1962 at age 19, Gingrich married his former high school geometry teacher, Jackie Battley, when she was 26. In the spring of 1980, Gingrich left Battley after having an affair with Marianne Ginther.

Gingrich and Ginther were married six months after Gingrich’s divorce from Battley in 1981. Then, in the mid-1990s, Gingrich began an affair with House of Representatives staffer Callista Bisek, who is 23 years younger than Gingrich.

Gingrich and Bisek continued their affair during the Monica Lewinsky scandal, when Gingrich became a leader of the investigation of President Bill Clinton for perjury and obstruction of justice in connection with his alleged affairs.

Gingrich married Bisek in 2000, shortly after his divorce from second wife Ginther.

In his response to The Family Leader, Gingrich also said he would “vigorously enforce” the Defense of Marriage Act (DOMA), which bans federal recognition of same-sex marriage. Earlier this year, President Barack Obama directed the Justice Department to cease defending the constitutionality of the law.

Also as part of his response, Gingrich said he would sign an executive order restating that federal funds should not be used to pay for overseas abortions and defend the First Amendment right to religious liberty.

Gingrich had declined to sign the group’s marriage pledge earlier this year because of his concerns with the wording of the pledge. He had said he would consider signing the pledge if some changes were made to it.

According to reports, Gingrich’s lesbian half-sister and gay rights activist Candace Gingrich-Jones is disappointed by Gingrich’s opposition to gay marriage.

Gingrich joined U.S. Rep. Michele Bachmann (R-Minn.), Texas Gov. Rick Perry and former U.S. Sen. Rick Santorum (R-Pa.) in signing The Family Leader’s pledge.

The Family Leader has yet to make an endorsement in the presidential race, but it said it has narrowed its list to Gingrich, Perry, Bachmann and Santorum.

In regard to Gingrich’s response, Bob Vander Plaats, president & CEO of The Family Leader, said: “We are pleased that Speaker Gingrich has affirmed our pledge and are thankful we have on record his statements regarding DOMA, support of a federal marriage amendment, defending the unborn, pledging fidelity to his spouse, defending religious liberty and freedom, supporting sound pro-family economic issues, and defending the right of the people to rule themselves.”

Following is the full text of Gingrich’s response to The Family Leader:

To Bob Vander Plaats and the Executive Board of The FAMiLY LEADER:

I appreciate the opportunity to affirm my strong support of the mission of the FAMiLY LEADER by solemnly vowing to defend and strengthen the family through the following actions I would take as President of the United States.

Defending Marriage. As President, I will vigorously enforce the Defense of Marriage Act, which was enacted under my leadership as Speaker of the House, and ensure compliance with its provisions, especially in the military. I will also aggressively defend the constitutionality of DOMA in federal and state courts. I will support sending a federal constitutional amendment defining marriage as the union of one man and one woman to the states for ratification. I will also oppose any judicial, bureaucratic, or legislative effort to define marriage in any manner other than as between one man and one woman. I will support all efforts to reform promptly any uneconomic or anti-marriage aspects of welfare and tax policy. I also pledge to uphold the institution of marriage through personal fidelity to my spouse and respect for the marital bonds of others.

Defending the Unborn. I believe that life begins at conception. On day one of my administration, I will sign an executive order reinstating Ronald Reagan’s Mexico City policy that prevents taxpayer dollars from being used to fund abortions overseas. I will also work with Congress to repeal Obamacare, defund Planned Parenthood so that no taxpayer dollars are being used to fund abortions but rather transfer the money so it is used to promote adoption and other pro-family policies, and enact legislation that provides greater protections for the unborn.

Defending Religious Liberty. As President, I will vigorously defend the First Amendment’s rights of religious liberty and freedom of speech against anyone who would try to stifle the free expression of believers. I will also promote legislation that protects the right to conscience for healthcare workers so they are not compelled to perform abortions and other procedures that violate their religious teachings.

Defending Against Debt. As President, I will undertake vigorous policies to maximize capital investment and job creation, along with common sense entitlement reforms, to dramatically turn around the nation’s fiscal situation. Building upon the same principles I championed during my four years as Speaker, when we reduced the national debt by over $400 billion and dramatically reduced the national debt as a percentage of the GDP, we will reduce the enormous burden upon American families of the public debt and unfunded liabilities.

Defending the Right of the People to Rule Themselves. Today, as federal courts have intervened in sectors of American life never before imaginable, including the intervention in the definition of marriage as well as when unborn life can be protected under the Constitution, the public has increasingly come to view them as an usurpative device for unelected rulers. This abuse of power and loss of public confidence amounts to a constitutional crisis. I believe the executive and legislative branches each have an independent responsibility to interpret the Constitution, and in those rare circumstances when they believe the federal courts, including the Supreme Court, have engaged in a serious constitutional error, they can choose among an array of constitutional powers to check and balance the courts. As President, I will nominate for federal judgeships, including justices of the Supreme Court, only those individuals who are committed to an originalist understanding of the Constitution. Judges with an originalist understanding will subordinate themselves to the meaning of the Constitution as it was intended by the framers, and not substitute their own judgments about its meaning. The inherent judicial self-restraint that comes from an originalist approach to the Constitution offers the best long-term assurance that federal judges will not exceed their powers and trample on individual liberties. I will also work with Congress to use the Constitutional means available to reassert the right of the elected branches of government to defend their understanding of the meaning of the Constitution, including limiting the jurisdiction of the federal courts to decide on certain issues, when they believe the federal courts have engaged in a serious constitutional error.